1. Field of the Invention
The present invention relates to a motion detection circuit for detecting motion from a television signal such as a MUSE signal.
2. Description of the Related Art
It is known that motion adaptive processes are performed in such circuits as Y/C separation circuits and non-interlace scanning converters. For example, interframe Y/C separation is performed for still pictures and interline Y/C separation is performed for moving pictures. Further, interfield scanning-line interpolation is performed for still pictures and interfield scanning-line interpolation is performed for moving pictures.
In order to perform such motion adaptive processes, it is required to detect motion from a television signal. FIG. 4 shows a prior art example of a motion detection circuit disclosed in ITEJ Technical Report Vol. 12, No. 51, PP. 1-6, TEBS 88-37 (November 1988).
Referring to FIG. 4, a television signal of NTSC system (NTSC signal) SV is input to an input terminal 41. While the NTSC signal SV is supplied to a subtractor 42 directly, it is supplied to the subtractor 42 also through a frame memory 43. The one-frame difference signal output from the subtractor 42 is supplied to a maximum value detection circuit 46 through a low-pass filter 44 and an absolute value circuit 45.
On the other hand, a color signal C (I signal, Q signal) is input to an input terminal 47. While the color signal C is supplied to a subtractor 48 directly, it is supplied to the same also through frame memories 49 and 50. The two-frame difference signal output from the subtractor 48 is supplied to the maximum value detection circuit 46 through a low-pass filter 51 and an absolute value circuit 52.
In the maximum value detection circuit 46, the maximum of the output signals of the absolute value circuits 45 and 52 is detected and it is supplied, as a motion information signal, to a coring circuit 53.
The NTSC signal SV input to the input terminal 41 is also supplied to a vertical edge detection circuit 58. The detection signal from the vertical edge detection circuit 58 is supplied to the coring circuit 53. In the coring circuit 53, a coring process (a process to vary the motion detection threshold value for preventing erroneous detection) is performed according to the magnitude of the vertical edge.
For example, when, as shown in FIG. 5A, there are an NTSC signal SV for a frame n (a signal before a shift indicated by the solid line) and an NTSC signal SV for a frame n+1 (a signal after a shift indicated by the broken line), the one-frame difference signal becomes as shown in FIG. 5B. As illustrated therein, the difference signal for the same shift amount becomes larger at the vertical edge portion. The same is true in the two-frame difference signal for the color signal C. Accordingly, the motion information signal for the same shift amount becomes larger at the vertical edge portion. Therefore, as described above, an adjustment is made in the coring circuit 53.
Referring back to FIG. 4, the motion detection signal output from the coring circuit 53 is supplied to an area filter 54. In the area filter 54, erroneously detected outputs which are produced incidentally from noises and the like are eliminated, taking it into consideration that motion of a picture occurs in a relatively large area. The area filter 54 is a kind of majority-decision circuit, in which the number of pixels in a block (m-dot.times.n-line) as shown in FIG. 6 which are decided to have been in motion are counted and the motion of a pixel under attention is judged by comparison of the count value with a preset threshold value.
For example, when a pixel under attention, which should have been in motion (solid circle), was detected and decided to have been at a standstill (open circle) due to noise or the like as shown in FIG. 7, it can be corrected to that in motion (solid circle) by a majority-decision process performed in the block for example of 3-dot.times.3-line (enclosed by the chain line).
The motion detection signal output from the area filter 54 is delivered to an output terminal 55 as a motion detection signal for Y/C separation. The motion detection signal output from the area filter 54 is also expanded in a temporal-spatial filter 56 in the directions of the horizontal, vertical, and time axes so as to prevent a motion to be detected from being missed, and then, it is delivered to an output terminal 57 as a motion detection signal for scanning conversion.
In the motion detection circuit of FIG. 4, the motion detection signal is expanded in the temporal-spatial filter 56 in the horizontal and vertical directions for preventing a motion to be detected from being missed. As a result, a detection spread to the still picture portion occurs and the picture quality is deteriorated.
For example, when the processing block of the filter 56 is 3-dot.times.3-line as shown in FIG. 8 (indicated by the chain line; the numerals attached are weighting factors), the motion detection signal of the pixel of the still picture (pixel under attention) located at the boundary between the area of still picture and the area of motion picture is effected by pixels in motion (solid circles) by insertion of the filter 56, though it should intrinsically be a pixel at a standstill (open circle).
Accordingly, it is intended in the present invention to prevent a motion to be detected from being missed without inviting the detection spread to the still picture portion.
An arrangement of the present invention is adapted therein such that a motion detection signal detected for each pixel is supplied to a maximum value calculation means performing calculation on the signal within a block of K-dot.times.L-line (K, L: natural numbers) and the output signal of the maximum value calculation means is supplied to a minimum value calculation means performing calculation on the signal within a block of M-dot.times.N-line (M, N: natural numbers), wherein the output signal of the minimum value calculation means is used as the motion detection signal of the arrangement.
By expanding a motion detection signal in the horizontal and vertical directions by making calculation in the maximum value calculation means within a block of K-dot.times.L-line, the missing of a motion to be detected is prevented. When a detection spread to a still picture portion occurs by performing the preventive process of the missing of a motion to be detected, the detection spread can be suppressed by making calculation on the signal in the minimum value calculation means within a block of M-dot.times.N-line.